Hydrocarbon oils, derived from paraffinic petroleum basestocks, and even from sources such as tar sands or shale oils, are useful for lubricants and specialty oils and even kerosene and jet fuels only when they have had their wax content reduced. Waxes present in such oils are detrimental to oil or fuel performance since if the oil or fuel is subjected to a low enough temperature environment the wax in the oil or fuel solidifies and forms, at best, a haze and, at worst, a high concentration of solid wax which detrimentally affects the pour point and flowability of the oil or fuel.
To this end, many processes have been developed to reduce the wax content of these hydrocarbon oils. At present, most hydrocarbon dewaxing is practiced utilizing solvent dewaxing processes. These processes are many and varied. Thus, dewaxing can be accomplished by mixing the waxy oil with liquid, normally gaseous autorefrigerative solvents, such as propane, butane, etc., and by reducing the pressure and lowering the temperature sufficiently to precipitate out the wax, which may then be separated from the dewaxed oil. Other dewaxing procedures utilized normally liquid dewaxing solvents, such as ketones (e.g., methyl ethyl ketone and methyl isobutyl ketone) and aromatic hydrocarbon (e.g., toluene) and mixtures of both (e.g., MEK/toluene). In procedures utilizing these solvents the oil is mixed with the solvent and chilled, either directly by using cold dewaxing solvent, or indirectly in indirect heat exchanger means, such as scraped surface chillers, to reduce the temperature and thereby precipitate wax from the oil.
These solvent dewaxing processes, while in themselves operable and efficient, have been improved by use of added dewaxing aids which act as nucleation centers for the wax during wax precipitation and result in production of wax particles which are more readily separable from the oil, i.e., waxes which can be filtered more efficiently from the oil as evidenced by improvements in feed filter rate and liquids/solids ratio of the dewaxed oil.
These dewaxing aids are high molecular weight polymeric materials and include chlorinated paraffins and naphthalene condensation products, polyalkyl acrylate and methacrylates, alkylfurmarates-vinylacetate copolymers, polyethylene oxides, polyvinyl pyrrolidiones, polyisobutylenes, alkali metal stearates, etc. These polymeric materials are of high molecular weight, ranging from 1,000 to 5,000,000, typically 2,000 to 1,000,000, more typically 5,000 to 500,000. They are used in amounts of from 0.01 to 5 weight percent active ingredient based on waxy oil, typically 0.01 to 2 weight percent, most typically 0.1 to 1.0 weight percent active ingredient based on waxy oil feed.
In general, these dewaxing aids are costly chemicals and, to the despair of refineries, have in the past been left in the wax or oil. Typical procedures for recovery of one material from another, such as distillation, have not usually been desirable or successful since the temperature employed in such distillation degrade the polymers, rendering the recovered material of rather limited usefulness. Vacuum distillation is more attractive and has been employed and is covered by U.S. Pat. No. 4,192,732. The disadvantage of even this successful process, however, resides in the fact that it employs distillation, which necessitates the expenditure of energy to heat the oil or wax to effect the separation of the dewaxing aid from said oil and/or wax and requires vacuum equipment.
It would be preferred if a non-degenerative process could be employed which is not energy intensive, which produces a stream of recovered dewaxing aid which has retained its potency and can be recycled for re-use to the solvent dewaxing process.
The use of membrane processes to separate oil and/or wax from dewaxing aid by permeation of the oil and/or wax molecules through a permeable selective membrane has been described in U.S. Ser. No. 588,236 now abandoned (see EP 84308369.2) and U.S. Ser. No. 666,385 now abandoned (see EP 84308368.4). These applications indicate that dewaxing aid can be recovered by permeation of oil/wax molecules through permselective membranes under ultrafiltration conditions and the recovered dewaxing aid retains its potency and can be recycled to the dewaxing process.
However, despite these showings of operability, it would be extremely desirable if the process could be made more efficient, if it could be run at higher temperature and/or higher pressure so as to achieve higher productivity, as well as securing a higher purity recovered dewaxing aid retentate.
To this end a new polymeric material has been identified and suitable membrane prepared which permits operation of the membrane separation ultrafiltration process at higher temperatures to achieve higher productivity.